The presnet invention relates to a method and apparatus for producing labels, more particularly to a method and apparatus for producing self-adhering lithographically printed labels.
In the packaging field there is a great demand for high quality pre-printed labels for labelling containers of various types. In order to facilitate the packaging and labelling of containers at a fast rate it is generally required that the labels to be attached to the containers be made available in a form in which they are easy to handle and easy to transfer onto the containers for which they are intended. In one convenient arrangement the labels are self-adhesive labels which are carried in series on a web of release material which is wound into a reel.
It is well known in the art to produce reels of self-adhesive labels carried on a release paper for transfer of the labels from the release paper to a container to be labelled.
One process for producing such labels is described in my company's U.S. Pat. No. 3,869,328. This patent describes a process for the production of a continuous reel of self-adhesive labels, wherein the labels are produced as separate flat sheets cut to finished size and stacked, the separate labels are then fed in succession from the stack onto the periphery of a drum and held thereon by vacuum means while being fed to an applicator by which they are coated individually on their reverse sides with a pressure-sensitive adhesive composition, the adhesive is dried by passing the labels through a hot air chamber extending around a substantial part of the periphery of the drum, and the labels are applied successively by their adhesive coated sides to a continuous web of release paper which moves against said drum and which is then reeled.
However this process has certain disadvantages in that it is difficult to produce a continuous reel of self-adhesive labels in which there is a regular gap between adjacent labels. Generally it is preferred to have a regular gap for ease of application of the labels to containers in a continuous labelling process. The reason for this difficulty is that it is not readily possible to place each successive label accurately onto the periphery of the rotating drum and then subsequently to transfer the labels accurately from the drum to the moving web of release paper to obtain a regular spacing between adjacent labels on the release paper. In addition, accurate alignment of the labels on the release paper can be difficult to achieve because of the difficulties mentioned above which are encountered when transferring the labels from the stack of labels to the release paper. This can result in some of the labels being skew relative to other labels on the reel of release paper. When the labels are subsequently applied to containers from the reel, any labels which are in a skew position on the reel of release paper are inevitably transferred in an out-of-true condition and are therefore mis-aligned on the container to which they are attached. This is unacceptable as it renders the product so labelled unattractive to the consumer.
A further disadvantage of this process is that after coating the reverse sides of the labels with pressure-sensitive adhesive, drying the adhesive and applying the labels by their adhesive coated sides to the continuous web of release paper, one frequently obtains surplus adhesive appearing around the periphery of the labels on the release paper. When the release paper is wound into a reel this surplus adhesive adheres to the back of the adjacent layer of release paper and can subsequently interfere with the unwinding of the reel and the application of the labels to containers to be labelled.
The present invention aims to overcome these disadvantages by arranging for the peripheral portions of labels applied to a support web to be removed after the labels have been applied to the support web and before the labels are wound into a reel.
As far as I am aware, in the past the printed matter carried on labels which are in the form of a continuous reel of self-adhesive labels is usually printed on to the labels in a continuous manner by means of flexographic, silk-screen, gravure or letterpress printing methods. However, all these printing methods have certain disadvantages when preparing printed labels carried in series on a support web intended to be wound into a reel. In particular, it is not possible to produce high quality multi-coloured images with screen-printing, flexographic, or letterpress printing techniques. The very nature of these printing techniques prevents them from being used to print fine screens. Furthermore, printing machines built to process labels on the reel are, of necessity, complicated and expensive to produce.
In addition very fine print cannot easily be reproduced if flexographic or screen printing techniques are used.
As a result of these various disadvantages, it has previously been difficult to obtain labels for containers having high quality print and showing multi-coloured images of high quality, except for labels printed by gravure techniques. However, owing to the high tooling costs associated with gravure printing, the use of gravure printing is limited to long printing runs.
Lithographically printed images do not suffer from the disadvantages of printed images prepared by the methods discussed above. The use of lithographically-printed images for the preparation of labels in reel form has, as far as I am aware, never been undertaken on a commercial scale, the main reason being that the printing cylinders used have to be specifically made for each different repeat length of label required. I believe that the problems associated with using lithographic printing processes have only been overcome on prototype equipment which lifts the printing cylinder and stops the web prior to each subsequent printing step.